The Challenges of Mobile Computing

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The Challenges of Mobile Computing

• George H. Forman, John Zhorjan

Alfred Park, Feb. 4, 2003
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The Future of Computing

• Its not just desktop computers anymore
• Steve Jobs recently stated that 2003 would be the
  Year of the Notebook and added that we want
  to replace even more desktops with notebooks
• Mobile computing is a building block for
  pervasive computing
• Calm Technology Mark Weiser
• Third Paradigm Alan Kay
• A little history first

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Its Been a Long Time Coming

• The Dynabook
• Conceived by Alan Kay, argued as the originator
  of the laptop concept
• Handheld, wireless connectivity, full multimedia
  capabilities, support for programming
• Circa 1972! Over 30 years ago

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The Dynabook
A portable interactive personal computer, as
accessible as a book
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The Vision is not a Reality Yet

• In a recent interview, Alan Kay remarked that
  even with the advent of PDAs, small notebooks,
  etc., the Dynabook concept is not a reality.
• Why?
• Todays technology path is not aligned with
  original spirit of the Dynabook concept
• Lacking technology
• We will examine the difficulties facing mobile
  computing due to technology constraints

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Mobile Computing ! Notebooks

• PDAs
• Cellular phones
• Tablet PCs
• Wearable computers

Apple Newton (1993)
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Tablet PC Demo Video

• Acer TravelMate C100 Tablet PC

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A New Paradigm

• tomorrows networked mobile computers are
  part of a greater computing infrastructure
• It will revolutionize the way computers are
  used
• Safe to say the paradigm shift has already begun

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Mobile Computing Properties

• Wireless Communication
• Network connectivity is essential for mobile
  computing platforms
• Mobility
• Issues relating to dynamic information change
• Portability
• What good is a device that only lasts 5 minutes
  on battery power?

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Wireless Communication

• Issues
• Lower bandwidth, higher error rates, signal path
  problems
• Increased communication latency, retransmissions,
  and timeout delays
• Mobility affords greater range of problems, e.g.
  moving from one coverage area to another

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Disconnection

• Two solution approaches
• (1) Prevent disconnections
• (2) Cope with disconnections
• For mobile computers, allowing disconnections to
  happen and recovering from them is the better
  solution
• Asynchronous operation (X11)
• Caching and reconciliation (Coda FS)

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Low Bandwidth

• There is a discernible difference in bandwidth
  between wireless and wired connections
• Two techniques to improve bandwidth
• (1) Install more wireless cells by overlapping
  cells on different wavelengths, or
• (2) reduce transmission ranges
• Other techniques compression and logging
• Available bandwidth is largely user-perceived, so
  tricks such as scheduling communication (lazy
  write-back and pre-fetching) to improve
  bandwidth utilization

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Security Risks

• Greater security risks than wired communication
• Solutions
• Hardware-based CLIPPER chip
• Software-based Kerberos authentication services

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Other Issues

• High bandwidth variability
• Applications should adapt to mobile devices
  changing from wired to wireless modes (and vice
  versa)
• Heterogeneous networks
• Moving from one service area to another

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Wireless Today

• IEEE 802.11 wireless standards
• a, b, d, e, f, g, h, i
• Up to 54Mbps transmission speeds (802.11a and
  802.11g), low bandwidth issue addressed with both
  solutions along with scaled bandwidth
• GPRS (2.5G) and UMTS (3G)
• Next generation cellular networks connecting
  cellphone users to the Internet
• Security issues
• WEP weak key vulnerability will be addressed in
  the 802.11i standard, which applies to the a, b,
  g physical standards

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Mobility

• The dynamic nature of mobile computing increases
  the volatility of information to support the
  platform
• Caching vs. recomputation

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Address Migration

• Current IP addressing scheme imposes difficulties
  for dynamically changing addresses
• Four different methods
• Selective broadcast
• Central services
• Home bases
• Forwarding Pointers

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Location Dependent Information

• Dynamic reconfiguration of local services and
  other location sensitive data requires the
  ability of mobile devices to reacquire this data
  that reflects the change in location
• Privacy issues mechanisms are needed to prevent
  users from snooping potentially sensitive data
  about other mobile users

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Mobility Today

• IP Mobility (Mobile IP) Draft Proposal
• Similar to the Forwarding Pointers method
• Fixed home address and a care-of address that
  changes at each new point of attachment

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Portability

• Mobile devices are fundamentally different from
  stationary machines such as desktop computers
• Must be designed with variety of constraints in
  mind, such as size and power consumption
  properties much like a wristwatch

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Low Power

• Tradeoff between battery weight (size) and
  battery life
• Power consumption proportional to CV2F
• C, Capacitance reduced by greater levels of VLSI
  and multichip modules
• V, Voltage reduced with chips and accessories
  requiring lower voltages
• F, Clock frequency reduced by scaling back clock
  rate when not needed
• Software mechanisms for power conservation, such
  as turning off backlights or spinning down hard
  disks

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Risks to Data

• Mobile devices are more prone to complete data
  loss
• Privacy concerns
• Solution Encryption, but is it feasible on a
  mobile computing platform?
• Data consistency
• Replicated file systems Coda FS

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Small User Interface

• Windowing systems/managers inadequate for small
  devices
• Favor recognition over keyboards or buttons
• Gesture, handwriting, and voice recognition
• Ambiguous input problematic
• Pen-based input

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Small Storage Capacity

• Hard Disks are a liability, PDAs use solid-state
  memory instead
• Use of distributed file systems and remote paging
  not applicable in most mobile computing scenarios
• Interpreted script languages provide an
  alternative to reducing compiled object code sizes

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Portability Today

• Intel XScale Architecture
• Low power consumption for amount of processing
  power provided
• IBM Microdrives
• Up to 4GB, low power consumption
• Large Solid-State Memories
• PDA, Cell phones
• Embedded wireless functionality (IrDA, Bluetooth,
  and 802.11)

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Relevance to Real-time Systems

• Mobility Depending on the requirements,
  deadlines could be driven by the correctness and
  validity of address or other information required
  for proper operation of the device (e.g. systems
  implementing the 802.11e QoS standard)
• Portability Hardware support for real-time
  operating systems in mobile computing RTOS must
  strike a balance between power consumption, ease
  of use, and features (e.g. servicing the GUI and
  the gesture / handwriting / voice recognition
  routines to provide a responsive environment)

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Video Augmented Surfaces

• Ubiquitous computing with mobile computers
• Using cameras and computers in the environment
  with portable notebooks to augment surfaces
• Jun Rekimoto of Sony CSL A Spatially Continuous
  Workspace for Hybrid Computing Environments